Aoc2020_Day23.scala

package aoc2020

import scala.annotation.tailrec

object Day23:
  type InputType = String

  @main def runDay23: Unit =
    val testData = time("testReady", () => ready(testInput))
    time("testPart1", () => part1(testData)) // should be 67384529
    time("testPart2", () => part2(testData))

    val data = time("ready", () => ready(input))
    time("part1", () => part1(data)) // 38925764
    time("part2", () => part2(data))

  private def ready(input: String): InputType =
    input

  private def part1(data: InputType): String =
    val result = move(100, data)
    val results = result.split("1")
    results.last + results.head

  @tailrec
  def move(cnt: Int, cups: String): String =
    if (cnt == 0) return cups
    val current = cups.head
    val tail = cups.tail.splitAt(3)
    val pickUp = tail._1
    val remain = tail._2
    val dest = remain.sorted.findLast(_ < current).getOrElse(remain.sorted.last)
    val parts = remain.split(dest)
    move(cnt - 1, parts.head + dest + pickUp + (if (parts.length > 1) parts.last else "") + current)

  private def part2(data: InputType): Long =
    0

  private val testInput = "389125467"

  private val input = "562893147"